Various chemical mechanical polishing (hereinafter referred to as “CMP”) aqueous dispersions that can chemically and mechanically polish a silicon oxide film, a polysilicon film, or the like at a practical polishing rate have been developed. On the other hand, most of the chemical mechanical polishing aqueous dispersions cannot polish a silicon nitride film at a practical polishing rate. Therefore, a method that removes a silicon oxide film formed on a silicon nitride film by CMP using the silicon nitride film as a stopper has been used. The silicon nitride film used as the stopper must be removed after removing the silicon oxide film.
However, when using a method that dissolves a silicon nitride film by using hot phosphoric acid and removes the silicon nitride film by etching, the silicon nitride film may remain or the lower layer of the silicon nitride film may be damaged since the etching treatment is controlled based on the etching time. Therefore, it is desirable to remove the silicon nitride film by CMP.
If the silicon nitride film can be removed by CMP using the silicon oxide film as a stopper, CMP can be applied to shallow trench isolation, self-aligned contact formation, and the like. Therefore, a high-performance device having high reliability can be produced.
In order to selectively remove the silicon nitride film by CMP, the polishing rate ratio of the silicon nitride film to the silicon oxide film (hereinafter simply referred to as “polishing rate ratio”) must be sufficiently increased.
JP-A-6-124932, JP-A-11-176773, and JP-A-2004-214667 disclose chemical mechanical polishing aqueous dispersions having an increased polishing rate ratio. However, these chemical mechanical polishing aqueous dispersions cannot achieve a polishing rate ratio sufficient for practical applications.